Why is synchronization used in Java and how does it affect thread operation?

Synchronization in Java is used to control access of multiple threads to shared resources to prevent data state issues (race conditions, inconsistency).

When multiple threads modify shared data simultaneously without synchronization, the result can be unpredictable. The synchronized keyword ensures that only one thread at a time executes a critical section of code.

Example of usage:

public class Counter {
    private int count = 0;

    public synchronized void increment() {
        count++;
    }

    public int getCount() {
        return count;
    }
}

Here, the increment method is synchronized, so if multiple threads call it simultaneously, they will execute sequentially, preventing loss of updates.

Thus, synchronization ensures correctness and predictability of multithreaded programs, but it can affect performance due to locking.